I often get loose stools/diarrhea this past summer and if i leave home before first bowel movement of day then i get horrible cramps, but fine after that. could it be an infection from receptive anal?

Yes: You need to see a doctor to be tested for intestinal parasites and other STDs. Please stop having risky sex. You are likely to get something much worse than diarrhea and cramps.

Multiple causes: Have an assessment by your physician. Something changed this summer. He/she will examine you and likely do a stool assessment. If necessary he/she will arrange for the area to be looked at by a colonoscopy. All the best sorting it out and I hope you feel better soon.